Figure 2. Polymer and nanocarbon materials molded in the VFD. (a) Crystallization and self-assembly of C60 under shear stress in toluene at a concentration below saturation level, resulting in (i) spicules, (ii) rods, and (iii) mixes of spicules and rods formed at 4000, 7000 and 6000 rpm, corresponding to specular flow, transitions from specular to double-helical flow and helical flow, respectively. (b) Creating (i) regular and (ii) irregular cones of self-assembled C60 in a 20 mm OD tube, with (iii) and (iv) being sharper pitch cones with extended arms in a 10 mm OD tube, formed by micro-mixing a 1:1 solution of C60 in o -xylene and DMF, θ 45°, 20 mm OD tube, with (v) Cones fastened to the wall of the glass tube, 10 mm OD tube. (c) (i and ii) Patterns of the holes arising from double-helical flow, formed at the interface of the glass tube and a thin polysulfone film (~ 5 µm) formed in toluene at 20°C, θ 45°, 7000 rpm rotational speed, along the length of the tube, with the arrow designating the direction of the rotational axis of the tube29. (d) Cartoon of the relative film thickness on the upper and lower side of the rotating hemispherical based quartz tube (20 mm OD, 17.5 mm ID) when processing a mixture of water and toluene; two types of fluid flows presented in the thin film were spinning top and double helical topological fluid flows. (e) Film thickness derived from neutron imaging. (f) Layer thickness as a function of height up the tube and rotational speed. (a-c) Reproduced under the terms of CC BY 3.0 license29. Copyright 2021, Royal Society of Chemistry. (d-f) Reproduced under the terms of Creative Commons Attribution 3.0 Unported License14. Copyright 2022, Royal Society of Chemistry.
We recently established that the VFD can centrifugally separate immiscible liquids of different densities in a θ 45° inclined rotating tube without using phase transfer catalysts, microgels, surfactants, complex polymers, nanoparticles, or micromixers14. Depending on the properties of the two liquids, the micro to submicron size topological flow regimes in the thin films discussed previously caused substantial inter-phase mass transfer. A Coriolis force is produced from the hemispherical base of the tube which is the spinning top topological fluid flow. This is present in the less dense liquid but penetrates the denser layer of liquid, transporting liquid from the upper layer through the lower layer to the surface of the tube. In a similar way, double helical topological flow in the less dense fluid caused by Faraday wave eddy currents being twisted by Coriolis forces, also impact of the surface of the tube. Through the self-assembly of nanoparticles at the interface of the two liquids, the lateral dimensions of these topological flows have been identified, Figure 3a. When a threshold rotational speed is achieved, double helical flow also occurs in the denser layer at high rotational speeds, which results in preformed emulsions of two immiscible liquids rapidly phase separating. By altering the shape of the base of the tube while maintaining rapid mass transfer between phases, it is possible to perturb the spinning top flow relative to double helical flow while avoiding the necessity for phase transfer catalysts, Figure 2d and 3b. The results discussed here have implications for overcoming mass transfer limitations at liquid interfaces and presenting innovative technologies for extraction and separation research, all while preventing the creation of emulsions.